Divicine and isouramil are naturally-occurring environmental chemicals that are found in fava beans (Vicia faba) as the pyrimidine beta- glucosides, vicine and convicine, respectively. These pyrimidine aglycones have been implicated as the causative factors in a life-threatening hemolytic anemia known as favism. Favism occurs after ingestion of fava beans by individuals who have a genetic deficiency in erythrocytic glucose 6-phosphate dehydrogenase (G6PD) activity. Although the mechanism of favism is not known, studies on the chemical reactivity of divicine have led to the hypothesis that these pyrimidines induce oxidative damage and initiate removal of sensitive red cells by splenic macrophages. However, several problems have hampered progress in this area: 1) there has been no animal model for G6PD deficiency; 2) only small amounts of divicine have been available to investigators, which has limited them to in vitro studies; and 3) the most commonly utilized method to prepare divicine was recently shown to degrade it, so the validity of much of the mechanistic literature is now in doubt. We have utilized a synthetic procedure to obtain gram amounts of divicine of high purity, and have shown, for the first time, that in vitro exposure of normal rat erythrocytes to divicine dramatically reduces their survival in vivo. More recent studies suggest that: 1) favism can be induced in the normal rat; 2) the level of reduced glutathione underlies the threshold for divicine toxicity; and 3) although human red cells with normal G6PD activity respond in a qualitatively similar manner, they appear to be Less sensitive to divicine than rat cells. The long-term goal of this research is to identify the mechanism of favism in humans. The aims of the present studies are: l) to determine the TD50 for divicine-induced hemolytic anemia in the rat, the fate of divicine- damaged erythrocytes in vivo, and the effect of G6PD inhibition and GSH depletion on the hemolytic response; 2) to synthesize isouramil and determine its hemolytic activity and potency relative to that of divicine; 3) to determine the stability of divicine in erythrocytes, identify the oxidative degradation products of divicine, and examine the role of free radicals in divicine-induced hemolytic anemia; and 4) To compare the responses of in vitro divicine exposure to rat and human erythrocytes in regard to: a) sulfhydryl status; b) morphology; c) membrane lipids and skeletal proteins; and d) immune system recognition.